In the field of printed electronics, comprising electrochemically active thin film devices based on organic electronics, it is known to provide flexible displays and structures by means of common printing techniques and equipment, such as screen printing, flexography, gravure, offset lithography and inkjet printing.
One type of flexible display is the fixed image display device, which upon activation is arranged to display one single fixed image. The image is fixed, hence, the fixed image display device is not arranged to display different, or moving, images as in the case of dynamic image display devices which comprise means or active control devices for addressing or switching separated portions of the dynamic image display device in order to change the displayed image or to display a different image. Instead, in the fixed image display device, the predetermined fixed image may be switched on or off, e.g. by application of an activation voltage between a pixel electrode and a counter electrode.
Compared to dynamic display devices the architecture of the electrochemically active and organic fixed image thin film display device is considerably simpler and allows for more cost effective manufacturing. In particular, the image to be displayed by the fixed image display device may be provided by e.g. patterning the active pixel electrode, or the electrolyte, into the desired fixed image. Hence, the fixed image is integrated into the device architecture of the fixed image display device, such that the fixed image is displayed upon activation of the device.
One example of a fixed image display device is illustrated and described in relation to FIGS. 16A to 16D in WO 2010/099147. As illustrated in FIG. 16B, the fixed image to be displayed by the display device is defined by providing an opacifier layer which is arranged to hide some details of the display device for the end user, such as a viewer or an observer of the display. In more detail, according to one example, the opacifier layer comprises a hole (e.g. hole 1631) which exactly matches the image to be presented to the end user. Hence, the fixed image to be displayed is defined by the gap in the opacifier layer. According to a second example, the opacifier layer comprises a hole (e.g. hole 1628) which is larger than the image shown to the end user. Instead, a chromic layer, illustrated in FIG. 16C, is patterned into, or given the same shape as, the fixed image shown to the end user (e.g. chromic layer 1606) since the opacifier layer in front of it does not create the image.
However, a drawback with known fixed image display devices based on layered electrochemically active and organic materials, is that the fixed image of the fixed image display device may be observed by the end user even before the application of an activation voltage. For example, differences in color, and/or reflection, between the opacifier layer and the chromic layer in the first example above, or between the chromic layer and the background layer in the second example above, may typically be detected by the end user. Hence, in other words, the fixed image of the fixed image display device is not truly hidden when the fixed image display device is turned off, or in its non-active state. In addition, high alignment requirements for manufacturing known fixed image display devices entail expensive and inefficient manufacturing processes involving e.g. exact matching of the opacifier layer in relation to the chromic layer.
The most apparent solutions to these problems would be to select a different material for the opacifier, or background layer, such that the difference in visual appearance between the chromic layer and the opacifier, or background layer, is minimized when the display is in a non-active state. Furthermore, known fixed image display devices based on layered electrochemically active and organic material normally suffer from non-uniform switching of the fixed image, as the switch of the electrochromic material normally starts at one end of the material and progresses throughout the remaining electrochromic material until the whole volume is switched.